Rubber compositions and pneumatic tires using the same

ABSTRACT

A rubber composition having improved weather resistance, thermal resistance, resistance to crack growth and wear resistance comprises not less than 20 parts by weight of a rubber composed mainly of ethylene, propylene and diene and satisfying all of particular requirements. Further, the rubber composition is applied to a tread and/or a sidewall of a pneumatic tire for improving a tire appearance.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a rubber composition containing rubbercomposed mainly of ethylene, propylene and diene and having improvedweather resistance, thermal resistance, resistance to crack growth andwear resistance. Further, it relates to pneumatic tires, particularlylarge size tires having considerably improved appearance and retreadinglife by using the above rubber composition in a tire sidewall as well aspneumatic tires having considerably improved appearance and resistanceto groove cracking by using the above rubber composition in a tiretread.

2. Related Art Statement

Heretofore, three has been developed a method wherein rubber composedmainly of ethylene and propylene is copolymerized with a thirdingredient such as dicyclopentadiene, ethylidene norbornene,1,4-hexadiene or the like for curing the rubber with sulfur. Theresulting terpolymer rubber (EPDM) has improved weather resistanoe andthermal resistance because there is no cutting of the main chain due tochemical attack of zone or the like owing to the absence of double bondsin the main chain.

However, the resistance to crack growth and wear resistance are fairlyinferior as compared with those of diene rubber. Further, the terpolymerrubber is poor in the covulcanizability with diene rubber and theapplication for rubber articles is considerably restricted.

In the field of pneumatic tires, the rubber composition for use in atire sidewall has frequently been composed of a blend of natural rubber,butadiene rubber (BR) and styrene-butadiene copolymer rubber (SBR).However, the use of BR having an excellent bending durability isincreasing as a recent trend. Furthermore, the blend of natural rubberand BR is dominant over the world, wherein the blending ratio of BRbecomes not less than 50%. Since the rubber composition composed of onlythe above diene rubber is easily apt to be oxidized by oxygen, ozone orthe like, it is usually compounded with a strong amine seriesantioxidant and a paraffinic wax for preventing the oxidation of therubber composition. In new tires made from the compounded rubbercomposition, there is no problem as to tne weather resistance, but theeffective amount of the antioxidant in the rubber composition isdecreased at the last use stage or in long-period use based on theretreading to cause ozone cracks and the like. The latter problem ishighlighted as the tire performances are considerably improved.

As countermeasures for solving this problem, there are considered amethod of increasing the amount of amine series antioxidant, a method ofusing an antioxidant having a long life, a method of using a reactiveantioxidant capable of reacting with a main chain of rubber, and so on.However, increasing the amount of amine series antioxidant results inonly slightly improved durability. Further, the use of a long-lifeantioxidant or reactive antioxidant only slightly improves age resistanteffect.

On the other hand, it has been attempted to use rubber containing no ora little diene ingredient and having substantially no double bond in itsmain chain (hereinafter referred to as non-diene rubber) so as not touse the antioxidant. Such a non-diene rubber includesethylene-propylene-diene terpolymer rubber (EPDM), halogenated butylrubber, chloroprene rubber and the like, but is rarely practised at thepresent because the bending durability and resistance to crack growthare considerably poor as compared with those of the diene rubber.

Lately, it is strongly demanded to improve the appearance of the tireitself in addition to the aforementioned problem. That is, when therubber composition for the tire sidewall contains large amounts of amineseries antioxidant and paraffinic wax as previously mentioned, theantioxidant and wax are bloomed on the rubber surface to form aprotective layer developing an excellent age resistant effect. However,when the protective layer is exposed to ultraviolet rays, the amineseries antioxidant is discolored brown to of considerably degrade thetire appearance. Particularly, in order to prevent the above phenomenonin tires for passenger cars, various studies have been made fromviewpoints of the improvement of antioxidant and the use of non-dienerubber, but there has not yet been effective prevention method.

Furthermore, the rubber composition for use in a tire tread hasfrequently been composed of a blend of natural rubber, BR and SBR. Incase of large size tires, since the ground contact pressure per unitarea at the tread surface is large and also the heat release value ofrubber is large, the tire tread is generally constructed with a rubbercomposition composed mainly of natural rubber having a small heatevolution and a large breaking strength. On the other hand, in the tiresfor passenger cars, the pressure at the tread surface and the heatrelease value are small as compared with those of the large size tire,and also the heat build-up is less because of the thin tread gauge.Therefore, in order to provide high traction, particularly high frictioncoefficient at wet state, the rubber composition for the tread of thepassenger car tire is composed mainly of SBR.

In the tire tread, the gripping property (particularly at wet state) andwear resistance are important properties, which have been improved byvarious methods up to date. However, weather resistance and resistanceto crack growth, which were insignificant in the past, cause a problemwith the improvement of wear resistance. This problem is a phenomenon ofproducing cracks in the groove bottom of the tread (i.e. groove crack).Such a phenomenon is observed in the tire, particulary after long use,when a greater part of the amine series antioxidant originally containedin the rubber composition has been consumed; this particularly become aserious problem at a high temperature area consuming a large amount ofthe antioxidant.

Many studies have been made in order to solve this problem. Forinstance, there have been attempted a method of increasing the amount ofamine series antioxidant used, a method of using non-diene rubbercomposition in a tread, a method wherein a thin rubber sheet having goodweather resistance is placed on the tread surface (because the surfaceportion of the tread is lost by wearing, while the groove portionthereof still remains at the last running stage) and so on. Among them,the increase of amine series antioxidant seems to be an immediatelyeffective method. However, it is very effective for the weatherresistance at initial running stage, but the effect of improving theweather resistance at last running stage is very small. This is due tothe fact that since the amine series antioxidant improving the weatherresistance is rapidly bloomed on the thread rubber surface to form theprotective layer as previously mentioned, even when the amount of theantioxidant added is made large, the thickness of the protective layer:s merely thickened and the holding time itself can not be prolonged.

As to the use of non-diene rubber composition, the development isbackward because the conventional non-diene rubber (e.g. butyl rubber,halogenated butyl rubber, EPDM, chlorosulfonated polyethylene rubber orthe like) is poor in wear resistance and is with difficulty in a treadrubber composition requiring weather resistance as an important factor.

In the case of placing the thin rubber sheet on the tread surface, theuse of non-diene rubber containing no double bond in its main chain iseffective as the thin rubber sheet having a good weather resistance, butthe adhesion to diene rubber (covulcanizability) is poor, so that thereis a problem that even if the rubber sheet is apparently adhered todiene rubber during a static test, peeling is caused therebetween due todynamic deformation suffered during the running of the tire.Consequently, the use of the thin rubber sheet is hardly practised.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a rubber composition whereinboth the resistance to crack growth and wear resistance are considerablyimproved as compared with those of the conventional EPDM rubbercomposition by controlling a microstructure of rubber composed mainly ofethylene, propylene and diene without greatly raising the iodine value.

It is another object of the invention to provide a pneumatic tirewherein the resistance to crack growth and weather resistance areconsiderably improved and the appearance is greatly improved by usingthe above rubber composition without substantially using an amine seriesantioxidant and a paraffinic wax.

According to a first aspect of the invention, there is the provision ofa vulcanizable rubber composition comprising not less than 20 parts byweight of a rubber composed mainly of ethylene, propylene and diene andsatisfying all of the following requirements:

(1) a glass transition temperature (Tg) of not higher than -50° C. asmeasured by a differential scanning calorimeter (DSC);

(2) an iodine value of 10˜34;

(3) a weight-average molecular weight of not less than 220,000;

(4) an ethylene content of 68˜85 mol %;

(5) a molecular weight distribution (Mw/Mn) of not less than 3.0;

(6) 95≦1.5×(iodine value)+(ethylene content)≦120; and

(7) 90≦(weight-average molecular weight)×10⁻⁴ +(ethylene content)≦110,

and 20˜150 parts by weight of an inorganic filler based on 100 parts byweight of rubber content.

According to a second aspect of the invention, there is the provision ofa pneumatic tire comprising a tread, sidewalls and bead portions; saidsidewall being constructed by using a rubber composition comprising notless than 20 parts by weight of a rubber composed mainly of ethylene,propylene and diene, not less than 10 parts by weight of an isoprenerubber, not less than 10 parts by weight of a process oil and 20˜100parts by weight of an inorganic filler based on 100 parts by weight ofrubber content.

According to a third aspect of the invention, there is the provision ofa pneumatic tire comprising a tread, sidewalls and bead portions; saidtread being constructed by using a rubber composition comprising notless than 20 parts by weight of a rubber composed mainly of ethylene,propylene and diene, not less than 10 parts by weight of a process oiland 50˜150 parts by weight of an inorganic filler based on 100 parts byweight of rubber content.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

According to the invention, the reason why the amount of the rubbercomposed mainly of ethylene, propylene and diene is limited to not lessthan 20 parts by weight is due to the fact that when the amount is lessthan 20 parts by weight, sufficient weather resistance and thermal agingresistance can not be obtained. The rubber composed mainly of ethylene,propylene and diene (hereinafter abbreviated as E/P rubber) according tothe invention has a characteristic that the weather resistance andthermal aging resistance are rapidly improved when the blending amountis increased to arrive at a range of 26˜30 parts by weight through thereason on such an improvement is not clear, so that the blending amountof the E/P rubber is preferably not less than 30 parts by weight. On theother hand, the reason why the amount of the inorganic filler is limitedto a range of 20˜150 parts by weight is due to the fact that when theamount of the inorganic filler is less than 20 parts by weight, thebreaking strength (strength at break, elongation at break) after thevulcanization of the rubber composition is insufficient, while when itexceeds 150 parts by weight, the processability at unvulcanized state isinsufficient.

The reason why the glass transition temperature of the E/P rubber isrestricted to not higher than -50° C. as measured at a temperaturerising rate of 10° C./min by DSC is due to the fact that when the glasstransition temperature is higher than -50° C., satisfactory resistanceto crack growth and bending durability can not be obtained. Furthermore,the restriction of iodine value to a range of 10˜34 is based on thefollowing fact. That is, when the iodine value is less than 10,sufficient covulcanizability with diene rubber, resistance to crackgrowth, strength at break and elongation at break can not be obtained,while when it exceeds 34, the effect of largely improving the resistanceto crack growth, strength at break and elongation at break can not beexpected and also the wear resistance after the thermal aging lowers.Moreover, a third ingredient used for enhancing the iodine value isgenerally expensive in the cost, so that the amount of the thirdingredient used is necessary to be reduced in the rubber compositionused for the manufacture of rubber articles as far as possible, which isalso true in the case of using the E/P rubber.

In the E/P rubber according to the invention, when the weight-averagemolecular weight is not less than 220,000, the effect of improving theresistance to crack growth and the wear resistance is conspicuous, andalso the adhesion strength to diene rubber is largely improved. However,as the molecular weight increases, the viscosity rapidly rises and theprocessability at unvulcanized state considerably degrades. Therefore,when the weight-average molecular weight exceeds 240,000, it ispreferable to subject the E/P rubber to an oil extension. In the lattercase, however, when the weight-average molecular weight exceeds 300,000,the amount of oil required for the processability is too large and theproperties after vulcanization such as wear resistance and the likelargely degrade. As the oil to be used in oil extension, paraffinic oilis favorable.

In the E/P rubber according to the invention, when the ethylene contentis within a range of 68˜85 mol %, satisfactory resistance to crackgrowth, strength at break and elongation at break are first obtained. Ifthe ethylene content is less than 68 mol %, even when the iodine valueis not less than 10, the effect of improving the resistance to crackgrowth, strength at break and elongation at break is very small, whileif it is higher than 85 mol %, the resulting E/P rubber substantiallycomes to polyethylene resin and is difficult to industrially use as arubber because the elongation at break is small and the modulus ofelasticity is high.

The reason why the molecular weight distribution (Mw/Mn) of the E/Prubber is limited to not less than 3.0 is due to the fact that when themolecular weight distribution (Mw/Mn) is less than 3.0, the rollprocessability is poor and the industrial use is difficult.

When the value of 1.5×(iodine value)+(ethylene content) is less than 95,satisfactory resistance to crack growth, strength at break andelongation at break are not obtained, while when it is more than 120,the thermal aging resistance (including the wear resistance after thethermal aging) lowers.

Further, when the value of (weight-average molecular weight)×10⁻⁴+(ethylene content) is less than 90, the covulcanizability with dienerubber and resistance to crack growth are insufficient, while when it ismore than 110, not only the processability (dispersibility of carbonblack and roll processability) is poor, but also the modulus ofelasticity of the rubber composition becomes too large and theindustrial use is difficult.

The reasons on the restrictions of the requirements as mentioned aboveexplain that the given properties of the E/P rubber are establishedwithin certain ranges defined in the above requirements. In other words,these reasons mean that the effect of the invention can not be obtainedwhen the requirements (1)-(7) are not simultaneously satisfied, becausethere are some synergistic actions among these requirements which havenever been known in the past.

The E/P rubber according to the invention may be produced by blendingsome rubbers composed mainly of ethylene and propylene. Such a blendcertainly exhibits good properties and naturally belongs to the categoryof the invention. However, when using the E/P rubber obtained bypolymerizing so as to simultaneously satisfy all of the requirements(1)-(7), the resulting rubber composition exhibits excellent properties(resistance to crack growth, wear resistance, strength at break,elongation at break and so on).

In the E/P rubber according to the invention, ethylidene norbornene(ENB) is preferably contained as a third ingredient in addition toethylene and propylene. However, the conventionally used thirdingredient such as dicyclopentadiene (DCP), 1,4-hexadiene or the likemay be used as much as the satisfactory resistance to crack growth,strength at break and elongation at break can be expected.

According to the invention, it is desirable that the amount of extenderoil contained in the E/P rubber is not less than 40 parts by weight.When the weight-average molecular weight of the E/P rubber is preferablynot less than 250,000 for sufficiently developing the effect of theinvention, if the amount of extender oil is less than 40 parts byweight, the processability is poor and the industrial use becomesdifficult.

In the rubber composition according to the invention, it is preferableto contain not less than 10 parts by weight, particularly not less than20 parts by weight of an isoprene rubber. When the amount of isoprenerubber is less than 10 parts by weight, the kneading operabilitydegrades and it is difficult to obtain sufficient rubber propertiesafter the vulcanization according to the compounding recipe. Further,the use of isoprene rubber is industrially favorable rather than the useof the obtain diene rubber from a viewpoint of securing the strength atbreak. The term "isoprene rubber" used herein means to include naturalrubber and synthetic polyisoprene rubber.

As the inorganic filler used in the rubber composition according to theinvention, carbon black is most preferable, but silicon dioxide(silica), calcium carbonate, titanium dioxide, zinc white and the likemay be used.

When the rubber composition according to the invention is applied to thetire sidewall, carbon black is preferable to have an iodine absorptionvalue of 35˜100 mg/g and a DBP oil absorption of 70˜140 ml/100 g. Whenthe iodine absorption value is less than 35 mg/g, it is difficult toobtain the desired strength at break, while when at exceeds 100 mg/g,the bending durability lowers. On the other hand, when the DBP oilabsorption is less that 70 ml/100 g, the dispersibility of carbon blackis insufficient, while when it exceeds 140 ml/100 g, the hardness afterthe vulcanization becomes too high and the bending durability degrades.

Furthermore, when the rubber composition according to the invention isapplied to the tire tread, carbon black is favorable to have an iodineabsorption value of 85˜200 mg/g and a DBP oil absorption of 100˜180ml/100 g. When the iodine absorption value is less than 85 mg/g and theDBP oil absorption is less than 100 ml/100 g, the wear resistance cannot be ensured, while when the iodine absorption value is more than 200mg/g and the DBP oil absorption is more than 180 ml/100 g, thedispersibility of carbon black can not be ensured.

Since the rubber composition according to the invention is considerablyexcellent in the weather resistance and thermal resistance as comparedwith the usually used diene rubber composition, it is not necessary touse an amine series antioxidant and a paraffinic wax. However, when theamount of the E/P rubber used according to the invention is as low as 20parts by weight, not more than 0.3 part by weight of amine seriesantioxidant and/or not more than 0.5 part by weight of paraffinic waxmay be added.

According to the invention, the hardness after the vulcanization of therubber composition constituting the tire sidewall (JIS spring typehardness, type A) is preferable to be within a range of 30˜60 in view ofthe bending durability and resistance to crack growth because thesidewall is subjected to a constant strain deformation. On the otherhand, the hardness after the vulcanization of the rubber compositionconstituting the tire tread (JIS spring type hardness, type A) ispreferable to be within a range of 55˜70. When the hardness is less than55, the cornering stability of the tire and the resistance to crackgrowth degrade, while when it exceeds 70, not only the resistance to ribtear and the bending durability but also the gripping property degrade,and it is difficult to ensure the sufficient braking performance.

The production of the E/P rubber used in the invention will be describedbelow.

That is, the E/P rubber according to the invention is produced, forexample, by adjusting ethylene, propylene and ethylidene norbornene as athird ingredient to a desirable composition and randomly copolymerizingthem in a hydrocarbon solvent in the presence of a catalyst consistingof (a) a soluble vanadium compound represented by a general formula ofVO(OR)_(n) X_(3-n) (wherein R is a hydrocarbon residue, X is a halogenatom and 0≦n≦3) or a vanadium compound represented by a general formulaof VX₄ and (b) an organic aluminum compound represented by a generalformula of R'_(m) AlX'_(3-m) (wherein R' is a hydrocarbon residue, X' isa halogen atom and 0≦m≦3).

As the vanadium compound represented by the above general formulae,mention may be made of VO(OCH₃)Cl₂, VO(OCH₃)₂ Cl, VO(OCH₃)₃, VO(OC₂H₅)Cl₂, VO(OC₂ H₅)₂ Cl, VO(OC₂ H₅)₃, VO(OC₂ H₅)₁.5 Br₁.5, VO(OC₃ H₇)Cl₂,VO(OC₃ H₇)₁.5 Cl₁.5, VO(OC₃ H₇)₂ Cl, VO(OC₃ H₇)₃, VO(O-n-C₄ H₉)Cl₂,VO(O-n-C₄ H₉)₂ Cl, VO(O-iso-C₄ H₉)Cl₂, VO(O-sec-C₄ H₉)₃, VO(OC₅ H₁₁)₁.5Cl₁.5, VOCl₃, VCl₄ and mixtures thereof. Among them, VO(OC₂ H₅)Cl₂ andVOCl₃ are particularly preferable.

As the organic aluminum compound, mention may be made of (CH₃)₂ AlCl,(CH₃)₁.5 AlCl₁.5, (CH₃)AlCl₂, (C₂ H₅)₂ AlCl, (C₂ H₅)₁.5 AlCl ₁.5, (C₂H₅)AlCl₂, (C₃ H₇)₂ AlCl, (C₃ H₇)₁.5 AlCl₁.5, (C₃ H₇)AlCl₂, (C₆ H₁₃)₁.5AlCl₁.5, (C₆ H₁₃)Al₂ Cl, (C₆ H₁₃)AlCl₂ and mixture thereof.

In the above catalyst, the ratio of organic aluminum compound tovanadium compound is within a range of 2˜50, preferably 5˜30 as anatomic ratio of Al/V.

The copolymerization may be carried out in a hydrocarbon solvent. As thehydrocarbon solvent, use may be made of aliphatic hydrocarbons such ashexane, heptane, octane, kerosine and the like; aromatic hydrocarbonssuch as benzene, toluene, xylene and the like; and mixtures thereof.

In the copolymerization reaction medium, the amount of the vanadiumcompound is 0.01˜5 millimol/l, preferably 0.1˜2 millimol/l.

The ethylene content of the E/P rubber may be varied by controlling thefeeding amount of ethylene in the copolymerization. However, it isindustrially difficult to obtain the ethylene content of more than 85mol %. (In laboratory, the ethylene content of more than 85 mol % can beachieved with the reduction of the yield.)

The polymerization temperature is 0°˜100° C., preferably 20°˜80° C., andthe polymerization pressure is 0˜50 kg/cm². Moreover, the adjustment ofmolecular weight is performed by using hydrogen.

The following examples are given in illustration of the invention andare not intended as limitations thereof.

PRODUCTION EXAMPLE

The rubber composed mainly of ethylene, propylene and diene (E/P rubber)according to the invention was produced as follows.

The copolymerization of ethylene, propylene and ethylidene norbornenewas continuously carried out in a stainless polymerization vessel of 15l capacity provided with a stirring device.

Hexane as a solvent was continuously charged at a rate of 5 l/hr intothe upper portion of the polymerization vessel. On the other hand, thepolymerized solution was taken out from the lower portion of thepolymerization vessel so as to always maintain 5 of the solution in thevessel. The catalyst composed of (a) VO(OC₂ H₅)Cl₂ and (b) (C₂ H₅)₁.5AlCl₁.5 was continuously charged into the upper portion of the vessel soas to maintain vanadium atomic concentration of 0.28 millimol/l andaluminum atomic concentration of 1.85 millimol/l in the vessel. Further,a mixed gas of ethylene and propylene (ethylene: 45 mol %, propylene: 55mol %) was charged into the upper portion of the vessel at a rate of 450l/hr, while ethylidene norbornene was charged at a rate of 25 g/hr.Moreover, a hydrogen gas was charged at a rate of 3.2 l/hr as a moleularweight adjusting agent.

The polymerization temperature was controlled to 41° C. through a jacketattached to the outer surface of the polymerization vessel. The pressureinside the vessel was 4.8 kg/cm².

The polymerized solution taken out from the lower portion of the vesselwas subjected to a steam stripping, dried at 80° C. over a night andthen dried under vacuum. Thus, rubber composed mainly of ethylene,propylene and diene (E/P rubber) was continuously obtained at a rate of265 g/hr as Sample-1.

Then, the weight-average molecular weight (Mw) and molecular weightdistribution (Mw/Mn) were measured by a gel permeation chromatography(GPC method), wherein the weight-average molecular weight was determinedby converting into polystyrene.

Further, E/P rubbers as Sample-2 to Sample-11 were produced by properlyvarying the amount of ethylene, amount of third ingredient, ratio ofAl/V in the catalyst, polymerization temperature, polymerization timeand the like.

The details of the thus obtained E/P rubbers are shown in the followingTables 1 and 2.

                                      TABLE 1                                     __________________________________________________________________________                      Ethylene  Amount of                                         Tg       Iodine                                                                            --Mw content   extender oil*                                                                          Third                                    (°C.)                                                                           value                                                                             (× 10.sup.4)                                                                 (mole %)                                                                           --Mw/--Mn                                                                          (part by weight)                                                                       ingredient                               __________________________________________________________________________    EP33  -55                                                                              22  17   65   3.5   0       ENB                                      EP43  -55                                                                               6  18   65   3.5   0       ENB                                      Sample-1                                                                            -60                                                                              15  25   77   4.0  30       ENB                                      Sample-2                                                                            -60                                                                               8  26   78   4.5  40       ENB                                      Sample-3                                                                            -46                                                                              25  22   50   3.5   0       ENB                                      Sample-4                                                                            -58                                                                              30  23   71   3.8  30       ENB                                      Sample-5                                                                            -69                                                                              37  18   72   2.2   0       ENB                                      Sample-6                                                                            -60                                                                              18  26   65   5.5  40       ENB                                      Sample-7                                                                            -59                                                                              18  24   75   2.3  30       ENB                                      Sample-8                                                                            -60                                                                              15  33   78   3.5  50       ENB                                      Sample-9                                                                            -60                                                                              18  26   83   3.5  40       ENB                                      Sample-10                                                                           -60                                                                              18  26   87   3.5  40       ENB                                      Sample-11                                                                           -60                                                                              15  26   78   3.5  40       DCP                                      __________________________________________________________________________     *The amount of extender oil is represented as part by weight per 100 part     of rubber composed of ethylene, propylene and diene.                     

                  TABLE 2                                                         ______________________________________                                        1.5 ×        (Weight-average molecular                                  (Iodine value) +   weight) × 10.sup.-4 +                                (Ethylene content) (Ethylene content)                                         ______________________________________                                        EP33    98             82                                                     EP43    74             83                                                     Sample-1                                                                              99.5           102                                                    Sample-2                                                                              90             104                                                    Sample-3                                                                              87.5           72                                                     Sample-4                                                                              116            104                                                    Sample-5                                                                              127.5          90                                                     Sample-6                                                                              92             91                                                     Sample-7                                                                              102            99                                                     Sample-8                                                                              100.5          111                                                    Sample-9                                                                              110            109                                                    Sample-10                                                                             114            113                                                    Sample-11                                                                             100.5          104                                                    ______________________________________                                    

In Tables 1 and 2, EP33 and EP43 are EPDM made by Japan Synthetic RubberCo., Ltd., respectively, and the extender oil is a paraffinic oil(non-staining) made by Idemitsu Sekiyu Kagaku K.K.

EXAMPLE 1˜2

Each of five rubber compositions having a compounding recipe as shown inthe following Table 3 was prepared in a Banbury mixer and vulcanized at145° C. for minutes. The properties of the resulting vulcanized rubberwere evaluated by the following test method.

(1) Resistance to crack growth

After a test piece of 60 mm×100 mm×1.0 mm was provided at its centerwith a scratch of 0.3 mm in length, it was subjected to an extensionfatigue cracking test at an oscillation number of 300 cycle/min under astrain of 50%, during which a time till growth up to 20 mm was measured.The resistance to crack growth was determined according to the followingequation and evaluated by an index value on the basis that the value ofcontrol (Comparative Example 1) was 100. ##EQU1## The larger thenumerical value, the better the resistance to crack growth.

(2) Wear resistance after thermal aging

An original specimen and a specimen obtained by leaving the originalspecimen in a thermostatic chamber of 120° C. for 24 hours weresubjected to an Akron type abrading test (load: 6 lbs, angle: 15° ,abrading number: 1,000 times), respectively, from which a ratio ofabrasion loss was calculated according to the oollowing equation:##EQU2## Then, wear resistance was evaluated by the following equation:##EQU3##

(3) Thermal aging resistance

An original specimen of 150 mm×150 mm×2.0 mm and a specimen obtained byleaving the original specimen in a thermostatic chamber of 120° C. for24 hours were subjected to a test for the measurement of strength atbreak, respectively, from which a ratio of strength at break wascalculated according to the following equation: ##EQU4## Then, thethermal aging resistance was evaluated by the following equation:##EQU5##

(4) Strength and elongation at break

They were measured according to JIS K6301. Moreover, the test piece hada shape of JIS No. 3.

(5) Weather resistance

A test piece of 20 mm×100 mm×1.0 mm was elongated to 50% and left tostand in a thermostatic chamber at 40° C. and an ozone concentration of50 ppm, during which a time till cracks were visually observed wasmeasured. Then, the weather resistance was evaluated according to thefollowing equation: ##EQU6## The larger the numerical value, the betterthe weather resistanoe.

The measured results are shown in Table 3. As seen from Table 3, therubber compositions of Examples 1 and 2 according to the invention areconsiderably excellent in the resistance to crack growth, thermal agingresistance, strength at break and elongation at break as compared withthe rubber compositions using the conventional rubber composed mainly ofethylene and propylene.

                                      TABLE 3                                     __________________________________________________________________________              Compar-                                                                             Compar-                                                                              Compar-                                                          ative ative  ative Example                                                                            Example                                               Example 1                                                                           Example 2                                                                            Example 3                                                                           1    2                                           __________________________________________________________________________    Natural rubber                                                                          50    50     50    50   50                                          BR01      50    --     --    --   --                                          EP43      --    50     --    --   --                                          EP33      --    --     50    --   --                                          Sample-1  --    --     --    65   --                                          Sample-11 --    --     --    --   70                                          Carbon black HAF                                                                        55    55     55    55   55                                          Aromatic oil *1                                                                         20    20     20    5    --                                          Stearic acid                                                                            2     2      2     2    2                                           Santoflex 13 *2                                                                         1     --     --    --   --                                          ZnO       3     3      3     3    3                                           CZ *3     0.5   0.8    0.8   0.8  0.8                                         TS *4     0.2   0.2    0.2   0.2  0.2                                         Sulfur    1.5   1.5    1.5   1.5  1.5                                         Weather resistance                                                                      100   *      *     *    *                                           Thermal aging                                                                           100   130    125   136  139                                         resistance                                                                    Resistance to                                                                           100   21     32    228  176                                         crack growth                                                                  Strength at break                                                                       100   65     34    100  98                                          Elongation at break                                                                     100   76     62    101  100                                         __________________________________________________________________________     Note:                                                                         *: No crack occurred even after 168 hours                                     *1: made by Fuji Kosan K.K.                                                   *2: antioxidant, N--(1,3dimethyl-butyl)-N'--phneylp-phenylenediamine          *3: vulcanization accelerator, N--cyclohexyl2-benzothiazylsulfenamide         *4: vulcanization accelerator, tetramethyl thiurammonosulfide            

EXAMPLES 3˜4

Each of ten rubber compositions having a compounding recipe as shown inthe following Table 4 was prepared in a Banbury mixer and thenvulcanized at 145° C. for 30 minutes. The properties of the resultingvulcanized rubber were measured in the same manner as described inExample 1, and the roll processability was visually evaluated. Themeasured results are also shown in Table 4. Moreover, the paraffinic oilwas the same as used as an extender oil in Production Example. InComparative Example 11, the resistance to crack growth, strength atbreak and elongation at break lowered because the modulus of elasticityof the rubber composition was high. It it apparent from Table 4 that theeffect of the invention can not be achieved unless the E/P rubbersimultaneously satisfies all of the requirements (1)˜(7).

                                      TABLE 4                                     __________________________________________________________________________              Compar-                                                                            Compar-                                                                             Compar-   Compar-                                                                             Compar-                                                                            Compar-                                                                            Compar-    Compar-                       ative                                                                              ative ative     ative ative                                                                              ative                                                                              ative      ative                         Example                                                                            Example                                                                             Example                                                                            Example                                                                            Example                                                                             Example                                                                            Example                                                                            Example                                                                             Example                                                                            Example                       4    5     6    3    7     8    9    10    4    11                  __________________________________________________________________________    Natural rubber                                                                          30   30    30   30   30    30   30   30    30   30                  SBR 1500  30   30    30   30   30    30   30   30    30   30                  BR01      40   --    --   --   --    --   --   --    --   --                  Sample-2  --   56    --   --   --    --   --   --    --   --                  Sample-3  --   --    40   --   --    --   --   --    --   --                  Sample-4  --   --    --   52   --    --   --   --    --   --                  Sample-5  --   --    --   --   40    --   --   --    --   --                  Sample-6  --   --    --   --   --    56   --   --    --   --                  Sample-7  --   --    --   --   --    --   52   --    --   --                  Sample-8  --   --    --   --   --    --   --   60    --   --                  Sample-9  --   --    --   --   --    --   --   --    56   --                  Sample-10 --   --    --   --   --    --   --   --    --   56                  Carbon black ISAF                                                                       45   45    45   45   45    45   45   45    45   45                  Paraffinic oil                                                                          16   --    16   4    16    --   4    --    --   --                  Stearic acid                                                                            2    2     2    2    2     2    2    2     2    2                   Santoflex 13                                                                            1    --    --   --   --    --   --   1     --   --                  ZnO       3    3     3    3    3     3    3    3     3    3                   CZ        0.6  0.8   0.8  0.8  0.8   0.8  0.8  0.6   0.8  0.8                 TS        0.2  0.2   0.2  0.2  0.2   0.2  0.2  0.2   0.2  0.2                 Sulfur    1.5  1.5   1.5  1.5  1.5   1.5  1.5  1.5   1.5  1.5                 Weather resistance                                                                      100  *     *    *    *     *    *    *     *    98                  Thermal aging                                                                           100  139   131  135  129   138  132  135   112  96                  resistance                                                                    Resistance to                                                                           100  48    24   215  158   96   186  169   105  64                  crack growth                                                                  Strength at break                                                                       100  68    60   102  99    89   93   95    100  75                  Elongation at break                                                                     100  65    72   100  98    88   100  92    98   69                  Wear resistance                                                                         100  126   122  115  86    116  114  126   128  126                 after thermal aging                                                           Roll processability                                                                     good good  good good good  good bad  bad   good good                                                          baggy                                                                              baggy                          __________________________________________________________________________     *No crack occurred even after 168 hours.                                 

EXAMPLES 5˜7

Each of five rubber compositions having a compounding recipe as shown inthe following Table 5 was prepared by using the E/P rubber of Sample-1in a Banbury mixer and then vulcanized at 145° C. for 30 minutes. Theproperties of the vulcanized rubber were measured in the same manner asdescribed in Example 1 to obtain results as shown in Table 5. In Table5, the amount of the E/P rubber based on 100 parts by weight of rubbercontent in Comparative Example 13 and Examples 5˜7 except the amount ofextender oil (30 parts by weight) were 15, 25, 40 and 80 parts byweight, respectively. As seen from the results of Table 5, the effect ofthe invention is first developed by using not less than 20 parts byweight of the E/P rubber according to the invention.

                  TABLE 5                                                         ______________________________________                                                         Com-                                                                   Compar-                                                                              par-                                                                   ative  ative   Ex-     Ex-   Ex-                                              Example                                                                              Exam-   ample   ample ample                                            12     ple 13  5       6     7                                      ______________________________________                                        Natural rubber                                                                            100      85      75    60    20                                   Sample-1    --       19.5    32.5  52    104                                  Carbon black HAF                                                                          50       50      50    50    50                                   Paraffinic oil                                                                            16       10      8.5   4     --                                   Stearic acid                                                                              2        2       2     2     2                                    Santoflex 13                                                                              1        --      --    --    --                                   ZnO         3        3       3     3     3                                    CZ          0.6      0.8     0.8   0.8   0.8                                  TS          0.2      0.2     0.2   0.2   0.2                                  Sulfur      1.5      1.5     1.5   1.5   1.5                                  Weather resistance                                                                        100      115     314   *     *                                    Thermal aging                                                                             100      106     117   127   137                                  resistance                                                                    Resistance to                                                                             100      99      186   265   201                                  crack growth                                                                  Wear resistance                                                                           100      97      104   108   108                                  after thermal aging                                                           Strength at break                                                                         100      97      101   100   101                                  Elongation at break                                                                       100      97      100   105   101                                  ______________________________________                                         *No crack occurred even after 168 hours                                  

A radial tire for passenger car having a tire size of 165 SR 13 wasmanufactured by applying each of the above five rubber compositions toeach of five parts equally divided on the circumfernece of the tiretread, which was run on an outdoor drum tester at a speed of 65 km/hrunder an internal pressure of 1.7 kg/cm² and a JIS 150% load over adistance of 150,000 km.

Thereafter, the occurrence of cracks produced in the groove bottom ofthe tread was observed to evaluate the weather resistance. As a result,cracks frequently occurred in the groove bottoms of the tread portionsmade from the rubber compositions of Comparative Examples 12 and 13,while no occurrence of cracks was observed in Examples 5˜7.

EXAMPLES 8˜10

Each of five rubber compositions having a compounding recipe as shown inthe following Table 6 was prepared in the same manner as described inExample 5, and then the dispersibility of carbon black, weatherresistance and strength at break were measured to obtain results asshown in Table 6. As seen from Table 6, when the amount of the inorganicfiller, i.e. carbon black is less than 20 parts by weight or more than150 parts by weight, the rubber composition is not durable in use.Particularly, the properties in Comparative Example 15 were notperformed because the dispersibility of carbon black was bad.

                  TABLE 6                                                         ______________________________________                                                                               Com-                                             Compar-                      par-                                             ative  Ex-     Ex-     Ex-   ative                                            Example                                                                              ample   ample   ample Exam-                                            14     8       9       10    ple 15                                 ______________________________________                                        Natural rubber                                                                            60       60      60    60    60                                   Sample-1    52       52      52    52    52                                   Carbon black HAF                                                                          18       25      100   140   160                                  Paraffinic oil                                                                            --       --      20    50    60                                   Stearic acid                                                                              2        2       2     2     2                                    Santoflex 13                                                                              1        --      --    --    --                                   ZnO         3        3       3     3     3                                    CZ          0.6      0.8     0.8   0.8   0.8                                  TS          0.2      0.2     0.2   0.2   0.2                                  Sulfur      1.5      1.5     1.5   1.5   1.5                                  Dispersibility of                                                                         good     good    good  accept-                                                                             bad                                  carbon black                       able                                       Weather resistance                                                                        *        *       *     *     --                                   Strength at break                                                                         65       100     174   120   --                                   ______________________________________                                         *No crack occurred even after 168 hours                                  

EXAMPLES 11˜12

A radial tire for passenger car having a tire size of 195/70 HR14 wasmanufactured by applying each of five rubber compositions having acompounding recipe as shown in the following Table 7 to each of fiveparts equally divided on the circumference of the tire sidewall, andthen the tire properties were evaluated as follows.

(1) Resistance to crack growth

After 20 scratches of 2 mm in width and 1.5 mm in depth were alternatelyformed on each divided part of the tire sidewall at angles of +45° and-45° with respect to the radial direction, the tire subjected to aninternal pressure of 1.7 kg/cm² was run on an indoor drum tester at aspeed of 65 km/hr under a JIS 100% load to measure a time till thescratch grew up to a length of 2.0 cm. The resistance to crack growthwas evaluated by the following equation: ##EQU7## The larger thenumerical value, the better the resistance to crack growth.

(2) Weather resistance

After the tire was actually run over a distance of 40,000 km, theweather resistance was evaluated by the presence or absence of cracks.

(3) Discoloration in sidewall

The degree of discoloration in the sidewall of the tire used in theevaluation of weather resistance before and after the running wasmeasured by means of a color difference meter of CR 100 type made byMinolta Camera Co., Ltd., from which a rise of lightness (ΔL) wascalculated. The larger the value, the larger the discoloration degree.

(4) Thermal aging resistance

The strength at break was measured with respect to an original specimenobtained by vulcanizing the rubber composition of Table 7 at 145° C. for30 minutes and a specimen obtained by leaving the original specimen in athermostatic chamber of 120° C. for 24 hours, from which a ratio ofstrength at break was calculated. Then, the thermal aging resistance wasevaluated according to the following equation: ##EQU8##

The reason why Santoflex 13 and paraffin wax were used as an antioxidantin Comparative Example 16 is due to the fact that the vulcanized rubberobtained by using a rubber composition of Comparative Example 16 exceptSantoflex 16 and paraffin wax was extremely poor in the weatherresistance after the evaluation in laboratory under conditions of ozoneconcentration of 50 pphm, 40° .C and an elongation strain of 20%. Asseen from Table 7, the rubber compositions containing the E/P rubberaccording to the invention are preferential in the weather resistanceand thermal aging resistance and considerably excellent in theresistance to crack growth as compared with the conventional EPDM rubbercomposition.

                  TABLE 7                                                         ______________________________________                                                         Com-    Com-                                                           Compar-                                                                              par-    par-                                                           ative  ative   ative   Ex-   Ex-                                              Example                                                                              Exam-   Exam-   ample ample                                            16     ple 17  ple 18  11    12                                     ______________________________________                                        Natural rubber                                                                            50       50      50    50    50                                   BR01        50       --      --    --    --                                   EP43        --       50      --    --    --                                   EP33        --       --      50    --    --                                   Sample-1    --       --      --    65    --                                   Sample-11   --       --      --    --    70                                   Carbon black                                                                              40       40      40    40    40                                   Li-HAF                                                                        Aromatic oil                                                                              20       20      20    5     --                                   Stearic acid                                                                              2        2       2     2     2                                    Santoflex 13                                                                              3        --      --    --    --                                   Paraffin wax                                                                              1        --      --    --    --                                   ZnO         3        3       3     3     3                                    CZ          0.5      0.8     0.8   0.8   0.8                                  TS          0.2      0.2     0.2   0.2   0.2                                  Sulfur      1.5      1.5     1.5   1.5   1.5                                  Weather resistance                                                                        fre-     *       none  none  none                                             quently                                                                       occurred                                                          Thermal aging                                                                             100      129     123   137   136                                  resistance                                                                    Resistance to                                                                             100      22      30    215   165                                  crack growth                                                                  Discoloration                                                                             7.8      1.5     1.5   1.0   1.0                                  ______________________________________                                         *No small crack occurred, but two large cracks (length: 1.8-2.5 cm)           occurred.                                                                

EXAMPLES 13˜14

A radial tire for truck and bus having a tire size of 1000 R 20 wasmanufactured by applying each of ten rubber compositions having acompounding recipe as shown in the following Table 8 to each of tenparts equally divided on the circumference of the tire sidewall, andthen the tire performances were evaluated in the same manner asdescribed in Example 11 to obtain results as shown in Table 8. In thiscase, the internal pressure of the tire was 7.5 kg/cm². Moreover, thestrength at break, elongation at break and roll processability wereevaluated in the same manner as described in Examples 1 and 3.

From the results of Table 8, it is understood that when the E/P rubbersimultaneously satisfies all of the requirements defined in theinvention, it exhibits satisfactory weather resistance, resistance tocrack growth, thermal aging resistance, strength at break and elongationat break and good roll processability as a rubber composition for tiresidewall so that it can industrially be used in the manufacture oftires.

                                      TABLE 8                                     __________________________________________________________________________              Compar-                                                                            Compar-                                                                             Compar-   Compar-                                                                             Compar-                                                                            Compar-                                                                            Compar-    Compar-                       ative                                                                              ative ative     ative ative                                                                              ative                                                                              ative      ative                         Example                                                                            Example                                                                             Example                                                                            Example                                                                            Example                                                                             Example                                                                            Example                                                                            Example                                                                             Example                                                                            Example                       19   20    21   13   22    23   24   25    14   26                  __________________________________________________________________________    Natural rubber                                                                          30    30   30   30   30    30   30   30    30   30                  SBR 1500  30    30   30   30   30    30   30   30    30   30                  BR01      40    --   --   --   --    --   --   --    --   --                  Sample-2  --    56   --   --   --    --   --   --    --   --                  Sample-3  --    --   40   --   --    --   --   --    --   --                  Sample-4  --    --   --   52   --    --   --   --    --   --                  Sample-5  --    --   --   --   40    --   --   --    --   --                  Sample-6  --    --   --   --   --    56   --   --    --   --                  Sample-7  --    --   --   --   --    --   52   --    --   --                  Sample-8  --    --   --   --   --    --   --   60    --   --                  Sample-9  --    --   --   --   --    --   --   --    56   --                  Sample-10 --    --   --   --   --    --   --   --    --   56                  Carbon black ISAF                                                                       45    45   45   45   45    45   45   45    45   45                  Paraffinic oil                                                                          16    --   16   4    16    --   4    --    --   --                  Stearic acid                                                                            2     2    2    2    2     2    2    2     2    2                   Santoflex 13                                                                            3     --   --   --   --    --   --   --    --   --                  Paraffin wax                                                                            1     --   --   --   --    --   --   --    --   --                  ZnO       3     3    3    3    3     3    3    3     3    3                   CZ        0.6   0.8  0.8  0.8  0.8   0.8  0.8  0.6   0.8  0.8                 TS        0.2   0.2  0.2  0.2  0.2   0.2  0.2  0.2   0.2  0.2                 Sulfur    1.5   1.5  1.5  1.5  1.5   1.5  1.5  1.5   1.5  1.5                 Weather resistance                                                                      frequently                                                                          none none none none  none none none  none slight                        occurred                                                            Thermal aging                                                                           100   137  130  136  128   136  134  135   114  97                  resistance                                                                    Resistance to                                                                           100   47   22   217  155   95   184  166   104  65                  crack growth                                                                  Strength at break                                                                       100   67   61   101  97    88   92   94    101  77                  Elongation at break                                                                     100   68   71   101  99    87   100  127   128  124                 Roll processability                                                                     good  good good good good  good bad  bad   good good                                                          baggy                                                                              baggy                          __________________________________________________________________________

EXAMPLES 15˜17

Each of five rubber compositions having a compounding recipe as shown inthe following Table 9 was prepared, which was applied to each of fiveparts equally divided on a circumference of a sidewall in a radial tirefor passenger car having a tire size of 165 SR 13. The properties of thetire were evaluated in the same manner as described in the previousexamples to obtain results as shown in Table 9. From the results ofTable 9, it is understood that the effect of the invention isconsiderably enhanced when the E/P rubber according to the invention isused in an amount of not less than 20 parts by weight.

                  TABLE 9                                                         ______________________________________                                                  Com-                                                                          par-  Compar-                                                                 ative ative    Ex-     Ex-   Ex-                                              Exam- Example  ample   ample ample                                            ple 27                                                                              28       15      16    17                                     ______________________________________                                        Natural rubber                                                                            100     85       75    60    20                                   Sample-1    --      19.5     32.5  52    104                                  Carbon black FEF                                                                          45      45       45    45    45                                   Paraffinic oil                                                                            16      10       8.5   4     --                                   Stearic acid                                                                              2       2        2     2     2                                    Santoflex 13                                                                              3       --       --    --    --                                   Paraffin wax                                                                              1       --       --    --    --                                   ZnO         3       3        3     3     3                                    CZ          0.6     0.8      0.8   0.8   0.8                                  TS          0.2     0.2      0.2   0.2   0.2                                  Sulfur      1.5     1.5      1.5   1.5   1.5                                  Weather resistance                                                                        fre-    fre-     none  none  none                                             quently quently                                                               oc-     occurred                                                              curred                                                            Thermal aging                                                                             100     106      117   127   137                                  resistance                                                                    Resistance to                                                                             100     99       186   265   201                                  crack growth                                                                  Wear resistance                                                                           100     97       104   108   108                                  after thermal aging                                                           Strength at break                                                                         100     97       101   100   101                                  ______________________________________                                    

EXAMPLES 18˜20

Each of four rubber compositions having a compounding recipe as shown inthe following Table 10 was prepared and vulcanized in the same manner asdescribed in Example 1, and thereafter the dispersibility of carbonblack, weather resistance and strength at break were measured in thesame manner as described in Example 1. Then, the above four rubbercompositions were applied to four parts equally divided on acircumference of a sidewall in a radial tire for passenger car having atire size of 165 SR 13, and then the resistasnce to crack growth of thesidewall was measured in the same manner as described in Example 11. Themeasured results are also shown in Table 10.

                  TABLE 10                                                        ______________________________________                                                  Comparative                                                                   Example  Exam-   Exam-                                                        29       ple 18  ple 19  Example 20                                 ______________________________________                                        Natural rubber                                                                            60         60      60    60                                       Sample-1    52         52      52    52                                       Carbon black GPF                                                                          18         25      90    110                                      Paraffinic oil                                                                            --         --      20    50                                       Stearic acid                                                                              2          2       2     2                                        Santoflex 13                                                                              3          --      --    --                                       Paraffin wax                                                                              1          --      --    --                                       ZnO         3          3       3     3                                        CZ          0.6        0.8     0.8   0.8                                      TS          0.2        0.2     0.2   0.2                                      Sulfur      1.5        1.5     1.5   1.5                                      Dispersibility of                                                                         good       good    good  acceptable                               carbon black                                                                  Weather resistance                                                                        frequently none    none  none                                                 occurred                                                          Strength at break                                                                         65         100     168   115                                      Resistance to                                                                             121        100     115   82                                       crack growth                                                                  ______________________________________                                    

As seen from Table 10, the rubber composition of Example 20 is somewhatlow in the resistance to crack growth and is not so suitable as a rubbercomposition for the sidewall subjected to a constant strain deformation.On the other hand, the rubber composition of Comparative Example 28,wherein the amount of inorganic filler was less than 20 parts by weight,is low in the strength at break and poor in the weather resistance, sothat it can not be used as a rubber composition for tire sidewall.

EXAMPLES 21˜24

Each of four rubber compositions having a compounding recipe as shown inthe following Table 11 was prepared and vulcanized in the same manner asdescribed in Example 1. The properties of the vulcanized rubber wereevaluated in the same manner as described in Example 1 to obtain resultsas shown in Table 11.

                  TABLE 11                                                        ______________________________________                                                  Example                                                                              Example  Example  Example                                              21     22       23       24                                         ______________________________________                                        Natural rubber                                                                            60       60       60     60                                       Sample-1    52       52       52     52                                       Carbon black HAF                                                                          45       --       --     --                                       Carbon black FEF                                                                          --       45       --     --                                       Carbon black GPF                                                                          --       --       45     --                                       Carbon black N683                                                                         --       --       --     45                                       Aromatic oil                                                                              15       15       15     15                                       Stearic acid                                                                              2        2        2      2                                        ZnO         3        3        3      3                                        DOTG *1     0.5      0.5      0.5    0.5                                      DM *2       0.6      0.6      0.6    0.6                                      Sulfur      1.5      1.5      1.5    1.5                                      Resistance to                                                                             114      100      100    82                                       crack growth                                                                  weather resistance                                                                        none     none     none   none                                     Roll processability                                                                       good     good     good   good                                     Dispersibility of                                                                         good     good     good   good                                     carbon black                                                                  ______________________________________                                         Note                                                                          *1 vulcanization accelerator, dio-tolylguanidine                              *2 vulcanization accelerator, dibenzothiazyldisulfide                    

For the reference, the iodine absorption value and DBP oil absorption ofeach of various carbon blacks are shown in the following Table 12.

                  TABLE 12                                                        ______________________________________                                                      Iodine                                                                        absorption                                                                              DBP oil                                               Carbon        value     absorption                                            black         (mg/g)    (ml/100 g)                                            ______________________________________                                        SAF           145       113                                                   LS-ISAF       118        78                                                   HS-ISAF       123       126                                                   ISAF          121       114                                                   N-231         125        91                                                   HS-HAF        90        124                                                   Li-HAF        68        104                                                   HAF           82        102                                                   FEF           43        121                                                   GPF           36         91                                                   N683          30        132                                                   N358          84        150                                                   ______________________________________                                    

EXAMPLES 25˜27

A radial tire for passenger car having a tire size of 175 SR 14 wasmanufactured by applying each of three rubber compositions havign acompounding recipe as shown in the following Table 13 to each of threeparts equally divided on the circumference of the tire sidewall.

The resistance to crack growth was measured with respect to theresulting tire in the same manner as described in Example 11. Moreover,the measurement of hardness was performed according to spring typehardness test (type A) of JIS K-6301. The measured results as shown inTable 13.

                  TABLE 13                                                        ______________________________________                                                  Example 25                                                                             Example 26 Example 27                                      ______________________________________                                        Natural rubber                                                                            20         20         20                                          Sample-1    104        104        104                                         Carbon black HAF                                                                          40         50         60                                          Aromatic oil                                                                              15         15         15                                          Stearic acid                                                                              2          2          2                                           ZnO         3          3          3                                           DOTG        0.5        0.5        0.5                                         DM          0.6        0.6        0.6                                         Sulfur      1.5        2.0        2.0                                         Hardness    57         62         67                                          Resistance to                                                                             100        58         39                                          crack growth                                                                  ______________________________________                                    

As seen from Table 13, sidewall rubber using the E/P rubber according tothe invention exceeds 60, the resistance to crack growth rapidly lowers,so that the hardness of the sidewall rubber is preferable to be not morethan 60. On the other hand, when the hardness is less than 30, the cutresistance of the sidewall rubber unfavorably and rapidly lowers.

EXAMPLES 28˜29

Each of five rubber compositions having a compounding recipe as shown inthe following Table 15 was prepared in a Banbury mixer. Then, a radialtire for passenger car having a tire size of 195/70 HR 14 wasmanufactured by applying each of the above five rubber compositions toeach of five parts equally divided on the circumference of the tiretread. The weather resistance, thermal aging resistance, resistance tocrack growth, wear resistance and adhesion to diene rubber wereevaluated with respect to the resulting tire to obtain results as shownin Table 15. In this case, the thermal aging resistance was measured inthe same manner as described in Example 1, the weather resistance wasmeasured in the same manner as described in Example 5, and the otherproperties were measured as follows.

(1) Resistance to crack growth

After five scratches of 2 mm in width and 1.0 mm in depth were formed onthe groove bottom of each of five divided tread parts, the tire was runon an indoor drum tester at a speed of 65 km/hr under an internalpressure of 1.7 kg/cm² and a JIS 100% load, during which a time till thescratch length grew to 1.5 cm was measured. The resistance to crackgrowth was evaluated according to the following equation: ##EQU9## Thelarger the numerical value, the better the property.

(2) Wear resistance

After the tire was actually run over a distance of 20,000 km, the depthof the remaining groove was measured at four positions, from which anaverage value was calculated. Then, a worn amount was calculated by(initial groove depth-average groove depth after running). The wearresistance was evaluated according to the following equation: ##EQU10##The larger the numerical value, the better the property.

(3) Adhesion to diene rubber

After the tire subjected to an internal pressure of 1.7 kg/cm² was runon an indoor drum tester provided with protrusions at a speed of 65km/hr under a JIS 150% load over a distance of 150,000 km, the presenceof peeling between the tire tread rubber and a tire tread base rubberhaving a compounding recipe as shown in the following Table 14 wasobserved, wherein smooth peeling at interface was evaluated asunacceptable and no smooth peeling was evaluated as good.

                  TABLE 14                                                        ______________________________________                                        Natural rubber (NR)                                                                              80 parts by weight                                         Polybutadiene rubber (BR)                                                                        20                                                         Carbon black HAF   35                                                         Santoflex 13       1                                                          Stearic acid       2                                                          ZnO                5                                                          CZ                 1.0                                                        Sulfur             2.5                                                        ______________________________________                                    

                                      TABLE 15                                    __________________________________________________________________________              Compar-                                                                             Comparative                                                                          Comparative                                                      Example                                                                             Example                                                                              Example                                                                              Example                                                                            Example                                              30    31     32     28   29                                         __________________________________________________________________________    Natural rubber                                                                          50    50    50    50   50                                           BR01      50    --    --    --   --                                           EP43      --    50    --    --   --                                           EP33      --    --    50    --   --                                           Sample-1  --    --    --    65   --                                           Sample-11 --    --    --    --   70                                           Carbon black ISAF                                                                       55    55    55    55   55                                           Aromatic oil                                                                            15    15    15    --   --                                           Stearic acid                                                                            2     2     2     2    2                                            Santoflex 13                                                                            1     --    --    --   --                                           Paraffin wax                                                                            1     --    --    --   --                                           ZnO       3     3     3     3    3                                            CZ        0.5   0.8   0.8   0.8  0.8                                          TS        0.2   0.2   0.2   0.2  0.2                                          Sulfur    1.5   1.5   1.5   1.5  1.5                                          Weather resistance                                                                      frequently                                                                          *     none  none none                                                   occurred                                                            Thermal aging                                                                           100   130   125   139  138                                          resistance                                                                    Resistance to                                                                           100   35    45    186  145                                          crack growth                                                                  Wear resistance                                                                         100   45    56    100  98                                           Adhesion to                                                                             --    unacceptable                                                                        unacceptable                                                                        good good                                         diene rubber                                                                            rubber                                                              __________________________________________________________________________     *No small crack occurred, but two large cracks (length: 1.8-2.5 cm)           occurred.                                                                

As seen from Table 15, the resistance to crack growth, wear resistanceand adhesion to diene rubber are considerably improved in the rubbercomposition containing not less than 20 parts by weight of the E/Prubber according to the invention as compared with the rubbercomposition containing the same amount of the conventional EPDM rubber.

EXAMPLES 30˜34

A radial tire for passenger car having a tire size of 165 SR 13 wasmanufactured by applying each of five rubber compositions having acompounding recipe as shown in the following Table 16 to each of fiveparts equally divided on the circumference of the tire tread, and thenthe resistance to crack growth and wear resistance were measured in thesame manner as described in Example 28 together with the rollprocessability and dispersibility of carbon black to obtain results asshown in Table 16.

                                      TABLE 16                                    __________________________________________________________________________                Example                                                                             Example                                                                             Example                                                                            Example                                                                             Example                                                30    31    32   33    34                                         __________________________________________________________________________    Natural rubber                                                                            60    60    60   60    60                                         Sample-1    52    52    52   52    52                                         Carbon black SAF                                                                          60    --    --   --    --                                         Carbon black LS-ISAG                                                                      --    60    --   --    --                                         Carbon black ISAF                                                                         --    --    60   --    --                                         Carbon black N-231                                                                        --    --    --   60    --                                         Carbon black HAF                                                                          --    --    --   --    60                                         Aromatic oil                                                                              15    15    15   15    15                                         Stearic acid                                                                              2     2     2    2     2                                          ZnO         3     3     3    3     3                                          DOTG        0.5   0.5   0.5  0.5   0.5                                        DM          0.6   0.6   0.6  0.6   0.6                                        Sulfur      1.5   1.5   1.5  1.5   1.5                                        Resistance to                                                                             101   96    100  114   100                                        crack growth                                                                  Wear resistance                                                                           115   88    100  96    85                                         Roll processability                                                                       acceptable                                                                          acceptable                                                                          good good  good                                       Dispersibility                                                                            acceptable                                                                          slightly                                                                            good acceptable                                                                          good                                       of carbon black   bad                                                         __________________________________________________________________________

EXAMPLES 35˜37

A radial tire for passenger car having a tire size of 175 SR 14 wasmanufactured by applying each of three rubber compositions having acompounding recipe as shown in the following Table 17 to each of threeparts equally divided on the circumfernece of the tire tread, and thenthe hardness and cornering stability were measured to obtain results asshown in Table 17. Moreover, the cornering stability was evaluated by afeeling of a driver when the tire was actually run on a circuit courseand a slalom course.

                  TABLE 17                                                        ______________________________________                                                  Example 35                                                                             Example 36 Example 37                                      ______________________________________                                        Natural rubber                                                                            20         20         20                                          Sample-1    104        104        104                                         Carbon black ISAF                                                                         45         50         60                                          Aromatic oil                                                                              15         15         10                                          Stearic acid                                                                              2          2          2                                           ZnO         3          3          3                                           DOTG        0.5        0.5        0.5                                         DM          0.6        0.6        0.6                                         Sulfur      1.5        1.8        2.0                                         Hardness    54         58         67                                          Cornering stability                                                                       bad        good       good                                        ______________________________________                                    

As seen from the results on the cornering stability in Table 17, thehardness of the tread rubber after vulcanization (JIS spring typehardness, type A) is preferable to be not less than 55 for theimprovement of the cornering stability.

As mentioned above, in the rubber composition using the E/P rubbersatisfying all of the requirements (1)˜(7) according to the invention,the resistance to crack growth, wear resistance, strength at break,elongation at break and adhesion to diene rubber are considerablyimproved as compared with the rubber composition using the conventionalEPDM rubber.

Furthermore, when the rubber composition according to the invention isapplied to the tire sidewall, the appearance is considerably improved.Moreover, when it is applied to the tire tread, the appearance and theresistance to groove cracking are considerably improved and theretreading life of large size tire is remarkably prolonged.Particularly, the rubber compositions according to the invention areapplicable to general rubber articles such as industrial belt, hose,rubber vibration isolator, marine fender and the like in addition to thepneumatic tires. Although a blend of ethylene-propylene series rubbersmay be used as an E/P rubber for satisfying the requirements (1)˜(7),the use of rubber polymerized so as to simultaneously satisfy all of therequirements (1)˜(7) exhibits more excellent properties such asresistance to crack growth, wear resistance and the like.

What is claimed is:
 1. A vulcanizable rubber composition comprising notless than 20 parts by weight of a rubber consisting essentially ofethylene, propylene and diene and satisfying all of the followingrequirements:(1) a glass transition temperature of not higher than -50°C. as measured by a differential scanning calorimeter; (2) an iodinevalue of 10˜34; (3) a weight-average molecular weight of not less than220,000; (4) an ethylene content of 68˜85 mol %; (5) a molecular weightdistribution (Mw/Mn) of not less than 3.0; (6) 95≦1.5×(iodinevalue)+(ethylene content)≦120; and (7) 90≦(weight-average molecularweight)×10⁻⁴ +(ethylene content)≦110,and 20˜150 parts by weight of aninorganic filler based on 100 parts by weight of rubber content.
 2. Therubber composition according to claim 1, wherein said rubber consistingessentially of ethylene, propylene and diene is compounded in an amountof not less than 30 parts by weight.
 3. The rubber composition accordingto claim 1, wherein said diene is ethylidene norbornene.
 4. The rubbercomposition according to claim 1, wherein said rubber consistingessentially of ethylene, propylene and diene is extended with an oil. 5.The rubber composition according to claim 1, wherein said compositioncontains not less than 10 parts by weight of an isoprene rubber.
 6. Therubber composition according to claim 1, wherein said compositioncontains not less than 20 parts by weight of an isoprene rubber.
 7. Therubber composition according to claim 4, wherein said oil is aparaffinic oil.
 8. The rubber composition according to claim 4, whereinsaid oil is used in an amount of not less than 20 parts by weight. 9.The rubber composition according to claim 1, wherein said inorganicfiller is carbon black, silicon dioxide, calcium carbonate or titaniumdioxide.
 10. The rubber composition according to claim 9, wherein saidcarbon black has an iodine absorption value of 35˜200 mg/g and a DBP oilabsorption of 70˜180 ml/100 g.